Hollow metal screw and method of making

ABSTRACT

A hollow screw and related process of making is provided, wherein the hollow screw is formed from a generally circular corrosion resistant stainless steel disk cut from flat roll stock. The hollow screw includes a head and an elongated and hollow shaft having a wall thickness between about 0.2 to about 0.7 millimeters extending therefrom and defining a shank portion and a threaded portion having a plurality of threads thereon with a rotational drive mechanism configured to facilitate tightening via the threads. The process involves annealing to soften the stamped hollow screw, followed by thread rolling, and then age hardening the hollow screw. As such, the resultant hollow screw is relatively lightweight, about 50% the mass of a solid core screw made from the same material, with a sufficient thread strength to meet most aerospace applications and contributes to important aircraft fuel economy.

BACKGROUND OF THE INVENTION

The present invention relates generally to a lightweight hollow metalstainless steel screw design particularly for use in aerospaceapplications, and a related method of making the hollow metal screw. Thehollow metal screw is produced by stamping from a generally circularsheet metal disk in one or more steps to form a hollow tubular head andscrew shank having a wall of thickness of from 0.2 to 0.7 millimeters.The screw shank is thereafter annealed to soften the screw shank forthread rolling, after which the hollow metal screw is hardenedsufficiently to meet aerospace thread strength requirements in a screwwhich is lighter than a similar size solid screw and thereforecontributes to aircraft fuel economy.

Screws are generally known in the art, and tend to comprise a solid coreshank upon which is rolled to form a set of screw threads of prescribedpitch and length. In general terms, a high strength corrosion resistantsteel (CRES) material is preferred as the screw material since threadsof hardened CRES can be repeatedly re-installed into a threaded borereceptacle without thread damage. Although, CRES constitutes arelatively heavy metal material and thus does not contribute to aircraftfuel economy, especially when the typical aircraft includes severalthousand such screws. Attempts to use lighter weight metals, such as asolid core aluminum or titanium screw, have met with limitations in theability for a mechanic to repeatedly install and remove the same screwwithout damaging the threads due to thread galling.

In the past, threaded screws have comprised solid cores, or a hollowscrew backstopped by a core insert of plastic or the like.Unfortunately, the plastic core insert is not without at least someweight addition, whereby the screw still is limited in its contributionto aircraft fuel economy.

The present invention comprises an improved hollow corrosion resistantmetal screw wherein the screw is stamped from a generally circular diskof a selected corrosion resistant metal material to provide a shank wallthickness of 0.2 to 0.7 millimeters, followed by annealing to soften themetal material, followed in turn by thread rolling and then by hardeningsteps to provide a hollow metal screw with a thread strength sufficientto withstand most aerospace applications, and to contribute to aircraftfuel economy by providing a hollow screw with corrosion resistant metalthreads wherein the hollow screw is approximately 50% the weight of asolid core screw made from the same material. The present inventionfulfills these needs and provides further advantages.

SUMMARY OF THE INVENTION

One embodiment of the hollow screw as disclosed herein includes a headand an elongated and hollow shaft integrally extending therefrom andformed from a flat stock of metal material. The elongated and hollowshaft includes a shank portion and a threaded portion having a pluralityof threads thereon. A rotational drive mechanism may be integrallyformed from the flat stock of metal material and coupled with the heador the elongated and hollow shaft, and configured to facilitatetightening of the hollow screw by way of the threads. In one embodiment,the rotational drive mechanism is a polygonal shape formed from the flatstock of metal material, wherein the polygonal shape may include anouter polygonal shape (e.g., a hexagon). Alternatively, the rotationaldrive mechanism may include an inner recess (e.g., a spline or cruciformrecess) formed from the head. Such a recess could be formed into a flathead or a rounded head.

In another aspect of this embodiment, an integral washer may be formedfrom the flat stock of metal material and extend outwardly from thehead. A captive washer may at least partially form around the integralwasher in a manner permitting free rotation of the captive washerrelative to the integral washer, the head, and the elongated and hollowshaft. More specifically, an outer rim of the captive washer may beturned upwardly and around an outer periphery of the integral washer toadjacently attach the captive washer about the integral washer, forsandwiching the integral washer therein. In one embodiment, the captivewasher may include a conductive material and have a thickness of about0.15 to 0.30 millimeters.

In other aspects of this embodiment, the hollow screw may include anelongated and hollow body having a constant diameter. In thisembodiment, the threads include an outer diameter relatively larger thanthe outer diameter of the relatively smooth shank portion. Here, a freefloating washer may be slidable along the shank portion and captivebetween the integral washer and the threaded portion, when added beforerolling the threads. Alternatively, the elongated and hollow body may beformed from a shank portion having a first diameter relatively largerthan a redraw portion having a second relatively smaller diameter,wherein the threads are imparted to the redraw portion during therolling step.

In one embodiment, the resultant hollow screw may be made from a flatstock of metal material that includes a corrosion resistant metalmaterial, such as A286 steel, wherein the elongated and hollow shaftincludes a wall thickness between about 0.2 to about 0.7 millimeters,yet the threads have a strength of about 1200 MPa to 1400 MPa and theweight of the hollow screw is approximately ½ the weight of a solidscrew of similar size and shape. Furthermore, a nose may be formed atone end of the elongated and hollow shaft opposite the head. In anotheraspect, the elongated and hollow shaft may also include a cap on one endopposite the head, the cap configured to prevent fluid flow through thebody of the hollow screw.

In another embodiment, the hollow screw as disclosed herein may includea head formed from a flat stock of metal material and an elongated andhollow shaft formed from the flat stock of metal material and integrallyextending from the head. In one embodiment, the elongated and hollowshaft may include a shank portion and a threaded portion having aplurality of threads thereon. Preferably, the threads have a strength ofabout 1200 MPa to 1400 MPa. The threaded portion may be relativelylonger than the shank portion, and the threads may have a major diameterrelatively larger than the diameter of the shank portion. Additionally,an integral washer may also be formed from the flat stock of metalmaterial and have an enlarged horizontal surface area radially extendingoutwardly from the head. A captive washer may be positioned underneaththe enlarged horizontal surface area and (optionally) have an outer rimbent generally about an outer periphery of the integral washer at leastpartially sandwiching the integral washer therein. In another aspect ofthis embodiment, a wave washer may be sandwiched by the captive washerand the enlarged horizontal surface area of the integral washer. Ineither embodiment, the captive washer may rotate freely relative to theintegral washer. To this end, a rotational drive mechanism integrallyformed from the flat stock of metal material and coupled with the heador the elongated and hollow shaft may be configured to facilitatetightening of the hollow screw by way of the threads, and about thecaptive washer.

In one embodiment, the shank portion and the threaded portion of theelongated and hollow shaft have a wall thickness between about 0.2 toabout 0.7 millimeters and the captive washer is made from a conductivematerial having a thickness of about 0.15 to 0.30 millimeters. Inanother embodiment, the rotational drive mechanism may include an outerpolygonal shape or an inner recess formed into the head from the flatstock of metal material, wherein the outer polygonal shape is a hexagonand the inner recess is a spline recess. Alternatively, the rotationaldrive mechanism may include an inner recess stamped into the bottom ofthe elongated and hollow shaft, and from the flat stock of metalmaterial. In this embodiment, a nose may be formed at this end,especially when the head is a round head or a flat head. Here, theelongated and hollow shaft is capped to prevent flow through the body ofthe hollow screw. Preferably, the flat stock of metal material is acorrosion resistant metal material, such as A286 steel.

In another embodiment, the hollow screw as disclosed herein may includea head formed from a corrosion resistant flat stock metal material suchas A286 steel. An elongated and hollow shaft having a wall thicknessbetween about 0.2 to about 0.7 millimeters may also be formed from thecorrosion resistant flat stock metal material and extend from the head.The elongated and hollow shaft preferably includes a shank portion and athreaded portion having a plurality of threads thereon, wherein thethreads have a strength between about 1200 MPa to 1400 MPa. The hollowscrew may further include a rotational engagement mechanism such as apolygonal shape or a recess formed from the head or the elongated andhollow shaft, and configured to permit tightening of the hollow screw byway of the threads. Preferably, the rotational engagement mechanism isalso formed from the corrosion resistant flat stock metal material andmay include a hexagonal head or a spline recess.

In another aspect of this embodiment, the hollow screw may furtherinclude an integral washer formed from the head and having an enlargedhorizontal and generally circular surface area radially extendingoutwardly from the head. A captive washer is then positioned adjacentthe enlarged horizontal surface area with an outer rim being bentgenerally about an outer periphery of the integral washer to at leastpartially sandwich the integral washer therein. The captive washer isable to rotate freely relative to the integral washer and the screwbody. In one embodiment, the captive washer may have a thickness of 0.15to 0.30 millimeters and be made from a conductive material. Furthermore,the elongated and hollow shaft may include a capped and tapered nosehaving a spline recess therein and be positioned at an end opposite thehead. In this aspect, the head preferably includes a round head, a flathead, or a tapered head, as opposed to a polygonal head, like theaforementioned hexagonal head.

One method for making the hollow screw as disclosed herein includessteps for forming a shallow cup having a radially outwardly extendingrough cut flange at one end thereof from a generally flat metalmaterial, such as a relatively circular blank stamped from a flat rollstock of corrosion resistant material, such as A286 steel. An elongatedand hollow body having a wall thickness of about 0.2 to about 0.7millimeters may be extruded from the shallow cup. Then, as part of aclipping and flattening step, the generally radially outwardly extendingrough cut flange may be trimmed and flattened to the desired size andshape of a screw head (e.g., a flat head or a round head). Next, thehollow screw may be annealed by heating the hollow screw for about 1hour at an elevated temperature of about 950-980 degrees Celsius tosoften at least the elongated and hollow body to a hardness of about 79Rockwell B. Thereafter, a plurality of threads may be rolled to at leasta portion of the exterior of the softened elongated and hollow body,thereby forming the elongated and hollow body into a substantiallysmooth shank portion and a threaded portion, before finally hardeningthe hollow screw by precipitation hardening for about 16 hours at atemperature of about 690-720 degrees Celsius in one finishing step. Inone embodiment, the hollow screw may have a final hardness of about 42Rockwell C and the threads may have a strength of about 1200-1400 MPa,and is about ½ the weight of a solid core screw of sufficient threadstrength.

Additionally, this method may include redrawing the elongated and hollowbody into a shank portion and a redraw portion having an outer diameterrelatively narrower than an outer diameter of the shank portion.Furthermore, the screw head may be inverted into a generally centralcurved dome with an outwardly extending skirt, and then reconed into anouter polygonal shape, and the skirt stamped into an integral washer.Additionally, a free formed washer may be formed into a captive washerover the integral washer. A spline or cruciform recess may further bestamped into the screw head as a rotational drive mechanism. During therolling step, a stability pin may be inserted into the elongated andhollow body. The stability pin preferably includes an outer diameterapproximately the size of an inside diameter of the threaded portion ofthe elongated and hollow body. Accordingly, the stability pin providessupport for the interior peripheral wall to prevent inward collapsingduring the rolling step. In other aspects of this method, a rounded nosemay be formed from one end of the elongated and hollow body and a bottomformed recess may be stamped into a closed end of the elongated andhollow body.

In another embodiment for a method of making the hollow screw asdisclosed herein, such method steps may include forming an elongated andhollow body having a wall thickness of about 0.2 to about 0.7millimeters from a generally flat metal material. Then, one end of theelongated and hollow body is clipped and flattened into a desired sizeand shape of a screw head. The hollow screw is then annealed for about 1hour at an elevated temperature of about 950-980 degrees Celsius tosoften the elongated and hollow body and the screw head. Next, aplurality of threads are rolled on to at least a portion of the exteriorof the softened elongated and hollow body, and the hollow screw isfinally hardened to a hardness of about 42 Rockwell C, wherein thethreads have a strength of about 1200-1400 MPa.

This method may further include the steps of stamping a relativelycircular blank from a flat roll stock of corrosion resistant material,such as A286 steel, redrawing the elongated and hollow body into a shankportion and a redraw portion having an outer diameter relativelynarrower than an outer diameter of the shank portion, inserting astability pin into the elongated and hollow body and then rolling thethreads onto the exterior or outer surface of the elongated and hollowbody. As mentioned above, the stability pin may have an outer diameterapproximately the size of an inside diameter of the threaded portion ofthe elongated and hollow body, so the stability pin can support theperipheral wall thereof to prevent collapsing when rolling the threads.

In other aspects of this method, the screw head may be inverted into agenerally central curved dome with an outwardly extending skirt. Next,the generally central curved dome may be reconed into an outer polygonalshape (e.g., a hexagon). Thereafter, the skirt may be stamped into anintegral washer wherein a free formed washer inserted over the elongatedand hollow body may have an outer rim bent over an outer periphery ofthe integral washer to at least partially sandwich the integral washertherein. Furthermore, a rotational drive mechanism may be imparted tothe hollow screw, such as by way of stamping a spline recess or acruciform recess to the screw head or keying a bottom formed recess intothe nose. In another aspect of this method, a rounded nose may be formedfrom one end of the elongated and hollow body.

Another method for making the hollow screw may include forming a shallowcup from a generally circular flat metal material and having a radiallyoutwardly extending rough cut flange at one end thereof, extruding anelongated and hollow body from the shallow cup, clipping and flatteningthe generally radially outwardly extending rough cut flange to thedesired size and shape of a screw head, inverting the screw head into acentral curved dome with an outwardly extending skirt, reconing thecentral curved dome into a polygonal shape, stamping the skirt into anintegral washer, annealing to soften at least the elongated and hollowbody, inserting a stability pin into the elongated and hollow body, thestability pin having an outer diameter approximately the size of aninside diameter of the elongated and hollow body to support theperipheral wall therein, rolling a plurality of threads to at least aportion of the exterior of the softened elongated and hollow body afterthe inserting step, stamping a spline recess to the screw head, andhardening the hollow screw.

Additionally, this method may include redrawing the elongated and hollowbody into a shank portion and a redraw portion having an outer diameterrelatively narrower than an outer diameter of the shank portion,stamping a relatively circular blank from a flat roll stock of corrosionresistant material comprising A286 steel, wherein the elongated andhollow body comprises a wall thickness of about 0.2 to about 0.7millimeters. Furthermore, the hollow screw may be heated for about 1hour at an elevated temperature of about 950-980 degrees Celsius, andprecipitation hardened for about 16 hours at a temperature of about690-720 degrees Celsius, wherein the hollow screw comprises a hardnessof about 42 Rockwell C and the threads comprise a strength of about1200-1400 MPa after the precipitation hardening step. Moreover, a washermay be inserted over the elongated and hollow body before the rollingstep, which allows the washer to free float between the integral washerand the threads. Also, a rounded nose may be formed from one end of theelongated and hollow body and keyed with a bottom mounted recess as arotational drive mechanism.

In another aspect of the embodiments disclosed herein, a hollow nut mayinclude a body having an internally threaded core and a first end havinga radially outwardly extending flange. A captive washer having an inneraperture with a diameter larger than the internally threaded core topermit insertion of a threaded fastener is at least partially formedaround the radially outwardly extending flange generally in adjacentrelationship with the first end and permitting free rotation relative tothe nut when attached thereto. In this embodiment, a wave washer mayalso be sandwiched between the captive washer and the first end havingthe radially outwardly extending flange. Preferably, the body is formedfrom a flat stock of metal material.

Another embodiment of the hollow nut includes a body having aninternally threaded core with at least one end having a radiallyextending flange, a wave washer positioned substantially adjacent the atleast one end, and a captive washer at least partially formed around theradially outwardly extending flange and generally sandwiching the wavewasher in between, wherein the captive washer is freely rotatablerelative to the wave washer and the radially extending flange.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a perspective view of one embodiment of the hollow screw asdisclosed herein;

FIG. 2 is a flow chart illustrating a series of process steps formanufacturing the hollow screw, such as those shown in FIGS. 1, 16-21and 25;

FIG. 3 is a fragmented perspective view illustrating an initial cuttingstep wherein a generally circular and flat blank is cut from a flatstock of metal material;

FIG. 4 is a fragmented perspective view wherein the circular blank isstamped into the shape of a shallow cup having an generally rough cutflange and an extruded cup body;

FIG. 5 is a fragmented perspective view illustrating an extrusion stepforming an elongated hollow body having a wall thickness on the order ofabout 0.2 to 0.7 millimeters;

FIG. 6 is a fragmented perspective view illustrating a redraw stepforming a reduced diameter or redrawn portion at a lower end of theelongated body;

FIG. 7 is a fragmented perspective view illustrating a clipping andflattening step to trim and flatten the head;

FIG. 8 is a fragmented perspective view illustrating an inversion stepforming a domed head with a downwardly projecting unfinished skirt;

FIG. 9 is a fragmented perspective view illustrating a recone stepforming a hexagonal head and integral washer;

FIG. 10 is a fragmented perspective view similar to FIG. 9, illustratinga stamping step forming an internal drive recess;

FIG. 11 is a fragmented perspective view illustrating a thread rollingstep;

FIG. 12 is a fragmented perspective view illustrating a mounting step,wherein a captive washer is stamped to the integral washer of the hollowscrew head;

FIG. 13 is a fragmented perspective view similar to FIG. 12,illustrating an alternative mounting step for stamping the captivewasher to the integral washer;

FIG. 14 is a fragmented perspective view illustrating a deformation stepto round off one end of the threaded hollow screw into a tapered nose;

FIG. 15 is a fragmented perspective view illustrating a step forstamping an internal bottom formed recess at the nose;

FIG. 16 is a partial cut-away perspective view of the hollow screw ofFIG. 1;

FIG. 17 is a partial cut-away perspective view of an alternative hollowscrew having a shorter elongated body relative to FIG. 16, a largerthreaded portion relative to the smooth shank portion, and a free formedwasher thereon;

FIG. 18 is a partial cut-away perspective view of an alternative hollowscrew having a flat head, rounded nose and internal bottom formed recessstamped therein;

FIG. 19 is a partial cut-away perspective view of an alternative hollowscrew similar to FIGS. 16 and 17, illustrating a substantially roundedhead in place of the hexagonal head;

FIG. 20 is a partial cut-away perspective view of another alternativeembodiment of the hollow screw and similar to FIGS. 1, 16 and 17,illustrating a standalone integral washer;

FIG. 21 is a partial cut-away perspective view of another embodiment ofa hollow screw in accordance with the embodiments disclosed herein,including a flat head mounted flush with a surface;

FIG. 22 is a cross-sectional view of one embodiment of the hollow screwhaving threads formed to the relatively narrower redrawn portion;

FIG. 23 is a cross-sectional view of another embodiment of the hollowscrew having threads formed to the constant diameter elongated body;

FIG. 24 is another cross-sectional view similar to FIG. 23, illustratingcaptive placement of the free formed washer between the integral washerand the threads;

FIG. 25 is a perspective view of the hollow screw of FIG. 1, furtherincluding a wave washer;

FIG. 26 is a cross-sectional view taken about the line 26-26 in FIG. 25with the addition of the captive washer, illustrating the sandwichedrelationship of the wave washer between the integral washer and thecaptive washer;

FIG. 27 is an alternative embodiment illustrating the captive washermounted to a nut; and

FIG. 28 is an embodiment similar to FIG. 27, illustrating the wavewasher sandwiched between the nut and the captive washer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the exemplary drawings, one embodiment of a hollow screw inaccordance with the present disclosure is referred to generally in FIG.1 by the reference numeral 10. As shown in FIG. 1, this embodiment ofthe hollow screw 10 includes an elongated body 12 (e.g., made from acorrosion resistant metal or steel material), having a smooth shankportion 14 and a threaded portion 16, having a plurality of threads 18thereon, a head 20, and a generally hollow interior identified as ahollow shaft 22 therein, which may be capped at one end to prevent fluidflow through the hollow shaft 22. In this embodiment, the hollow screw10 further includes an integral washer 24 preferably generally formedfrom a portion of the head 20 and a captive washer 26 that mayoptionally be added to the hollow screw 10, during a stamping step, asdescribed in more detail below. The captive washer 26 may rotate freelyrelative to the integral washer 24 to prevent the head 20 of the hollowscrew 10, and specifically the integral washer 24, from digging into theouter mounting surface where the hollow screw 10 may be inserted andused, as in the case of aerospace applications. In this embodiment, thehead 20 is in the shape of a hex nut and may be used alone or incombination with an inner recess 28, such as a spline or cruciformrecess or indentation, for purposes of rotationally tightening thehollow screw 10, in accordance with known tools and the embodimentsdisclosed herein.

The thus resultant hollow screw 10 may include a lightweightconstruction which is easy to install, remove, and re-install, and whichcontributes significantly to overall fuel economy of the aircraft.Moreover, the threaded portion 16 and specifically the threads 18 arepreferably capable of meeting most aerospace strength requirements in anacceptable fashion. To this end, the hollow screw 10, and the relatedmethod steps for making the screw 10, and its variations shown, e.g., inFIGS. 16-25, are generally shown in the flowchart of FIG. 2, and morespecifically with respect to FIGS. 3-15. The hollow screw 10 providessubstantial thread strength to resist galling on removal or onreinstallation, and which is about ½ the weight of a solid screw.

With respect to the manufacturing process, FIG. 2 is a flow chartillustrating the general process (200) for forming one or morevariations of the hollow screw 10, as disclosed herein. For example, ina first step (202), a flat strip of stainless steel feed stock 30, suchas A286 corrosion resistant steel or the like, may initially be fed intoa punch press or the like (shown generally in FIG. 3) to cut a pluralityof circular blanks 32 with a punch 34. Each circular blank 32 is thenstamped as part of step (204) using one or more formations that may useone or more stamping tools 36, of the type generally shown in FIG. 4,into a shallow cup 38 of selected size and shape. The shallow cup 38illustrated in FIG. 4 includes a generally radially outwardly extendingrough cut upper flange 40 and relatively short extruded cup body 42. Theshallow cup 38 is then processed as part of an extrusion step (206) inFIG. 5 wherein the length of the extruded cup body 42 is lengthened inone or more formations into the approximate size and shape of theelongated body 12 of the final hollow screw 10 by an extrusion tool 44.Of course, the extrusion step (206) may use one or more extrusion tools44 that vary in size and shape depending, of course, on the final sizeand shape characteristics of the hollow screw 10, and as part of one ormore formations, to obtain the desired work piece 46 suitable for thenext step (208).

In this respect, the next redraw step (208) is optional. Step (208), asshow in more detail in FIG. 6, includes redrawing a relatively narrow orredrawn portion 48 from the otherwise consistent diameter elongated body12, as shown in a work piece 46′. Step (208) basically separates theelongated body 12 into two primary portions, the smooth shank portion 14and the relatively narrower and still smooth redraw portion 48, as shownin FIG. 6. Whether step (208) is performed is dependent on whether theresultant thread portion 16 is to have the threads 18 of the same (FIG.22) or larger (FIGS. 23 and 24) outer diameter relative to the smoothshank portion 14, as described in more detail below. Although,preferably, the entire elongated body 12 has a wall thickness on theorder of about 0.2 to about 0.7 millimeters, even though the outerdiameter of the smooth shank portion 14 may be different than the outerdiameter of the redraw portion 48 (and eventually the resulting threads18).

The next clipping step (210) is compatible with both variations asdescribed above, i.e., the work piece 46 having the constant diameterelongated shank 12 (not shown in FIG. 7) or the work piece 46′ havingthe elongated shank 12 with the redraw portion 48 (shown in FIG. 7). Ingeneral, subsequent steps (212)-(228) are also compatible with both workpieces 46, 46′. The only differences are with respect to the outerdiameter of the shank portion 14 relative to the threaded portion 16,and specifically the threads 18, as shown and described in more detailbelow with respect to FIGS. 22-24. In step (210), the head 20 isillustrated being clipped and flattened. As viewed in FIG. 7, the roughcut flange 40 can be trimmed to an overall desired size and shape andflattened by a single stamping tool 50, or by clipping the work piece46, 46′ in one step with one tool, and stamping the work piece 46, 46′in another step with another tool. Of course, the clipping and stampingstep may involve multiple formations. To this end, either way, the roughcut flange 40 is cut away from the head 20 and the head 20 is stampedinto a generally flat head 54. FIG. 7 illustrates a roughened outer edgeportion 52 cut-away from the head 20 and being discarded therefrom. Theflat head 54 may be the same or substantially similar to the flat head54 shown in the final hollow screw 10″ of FIG. 18. The underlying toolblank 56 is shown having a shape and structure to accommodate insertionof the work piece 46′ with the elongated body 12 having the shankportion 14 and the relatively narrower redraw portion 48, but the toolblank 56 could be changed out for one that includes a constant diameterto match the size and shape the work piece 46 having the constantdiameter elongated body 12, or any other such embodiment with varioussizes, shapes and/or diameters.

The next step (212) as shown in the flowchart of FIG. 2 is to invert theflattened head 54 to form a generally inverted central curved dome 58 asgenerally shown in FIG. 8. The full size and shape of the curved dome 58may be accomplished in one or more formations as part of the inversionstep (212), depending on the desired shape and size of the curved dome58. Additionally, FIG. 8 illustrates a generally outwardly extendingskirt 60 formed at the bottom of the curved dome 58. The skirt 60 may beformed into the aforementioned integral washer 24, as briefly mentionedabove, in subsequent steps or multiple formations as described herein.Similarly, this step (212) may be used with the work pieces 46, 46′.

The next step (214) is to optionally recone the curved dome 58 into anouter polygonal shape 62, as shown in FIG. 9, with a stamping tool 64 ofreciprocal size and shape. Similarly, step (214) may be accomplished inone or more formations, depending on the size, shape and desiredapplication of the finished product. In the embodiment shown in FIG. 9,the curved dome 58 is stamped into a standard polygonal shape 62 ofselected size and shape (e.g., hexagonal) for use with a hex wrench orthe like. Although, the curved dome 58 may be stamped into other keyedshapes or polygons, as may be known in the art and suitable for turningby a standard key or the like. Of course, the polygonal shape 62 may beany shape or size known in the art to provide keyed rotation of thehollow screw 10. Also as part of step (214), and as part of one or moreformations, the outer skirt 60 may be generally formed into the size andshape of the integral washer 24, as shown herein with respect to FIGS.1, 16, 17 and 20.

In addition to or instead of step (214), the inner recess 28 may beformed as part of step (216). For example, FIG. 10 illustrates the head20 being stamped by a spline stamp 66 forming the interior surfacethereof into the shape of the inner-formed recess 28. In thisembodiment, the inner recess 28 is the size and shape of a spline recesssuitable for turning by a standard spline key or the like. Of course,the inner recess 28 may be any shape or size known in the art to providekeyed rotation of the hollow screw 10. The hollow screw may include onlythe outer polygonal shape 62 (e.g., FIG. 25), only the inner recess 28(e.g., FIGS. 19 and 21), a combination of the outer polygonal shape 62and the inner recess 28 (e.g., FIGS. 1, 16, 17, and 20), or none of theabove (e.g., FIG. 18), as described in more detail below.

In one embodiment, the next step (218) may be to anneal the thus-farformed hollow screw work piece to soften the corrosion resistant steelmaterial for thread rolling. In one embodiment, the annealing step (218)may be performed in a heat treatment for about 1 hour at an elevatedtemperature of about 950-980 degrees Celsius. The elongated body 12,including only the shank portion 14 in some embodiments or the shankportion 14 and the redraw portion 48 in other embodiments, may include ahardness of about 79 Rockwell B at the end of the annealing step (218).

At this point, the threads 18 may be roll formed as part of step (220),as shown in FIG. 11. In one embodiment, as shown in FIG. 11, the threads18 are roll formed to the redraw portion 48 of the elongated body 12 byway of at least a pair of thread rolling dies 68. Although, step (220)may be performed with any number of rolling dies 68, such as three ormore, as needed. Additionally, step (220) may include deployment of astability pin 70 into the hollow shaft 22 during the rolling step (220)for stabilization therein and to prevent the peripheral wall of theredraw portion 48 from collapsing into the interior of the hollow shaft22. In this respect, the stability pin 70 preferably has an outsidediameter approximately the size as the inside diameter of the hollowshaft 22. Accordingly, the formed threads 18 preferably have the samewall thickness as the shank portion 14, namely, about 0.2 to about 0.7millimeters.

Following the rolling of the threads 18 in step (220), the entire hollowscrew 10″″ is precipitation hardened by heat treatment for about 16hours at an elevated temperature of about 690-720 degrees Celsius duringstep (222), to provide a hollow screw 10″″ having a hardness on theorder of about 42 Rockwell C. The strength of the threads 18 is on theorder of about 1200 megapascals (“MPa”) to about 1400 MPa, andpreferably 1300 MPa, suitable for most aerospace applications. As such,FIG. 11 illustrates one embodiment of a finished stainless steel hollowscrew 10″″ (FIG. 20) ready for use.

Although, in another alternative embodiment, the hollow screw 10″″ couldbe fitted with an optional washer, such as the captive washer 26 (FIG.1), as shown in FIG. 12 with respect to step (224) in FIG. 2. Here, afree formed washer 72 having an aperture 74 with a diameter slightlygreater than the outer diameter of the threads 18 is able to slide on tothe hollow screw 10″″ and along the length of the elongated body 12 tothe position shown in phantom in FIG. 12. This configuration is nowcommensurate in scope with the hollow screw 10′ illustrated in FIG. 17,and may be used as described herein. Although, the potential drawback ofthis embodiment is that the free formed washer 72 may fall off thelength of the elongated body 12.

Alternatively, the hollow screw 10′ and the free formed washer 72 may beloaded together for press fit engagement by another tool 76, wherein anouter rim 78 of the free formed washer 72 is turned upwardly to fitrelatively closely with the integral washer 24. This embodiment is shownwith respect to the hollow screw 10 in FIG. 12. Here, the integrallyformed head 20 and the elongated body 12 are able to rotate relative tothe now mounted captive washer 26. Mounting (224) of the outer rim 78 ofthe free formed washer 72 over the integral washer 24 of the head 20 maytake place in a conventional assembly press (shown generally in FIG. 12)or the like. The optional captive washer 26 may be relatively thin,e.g., on the order of about 0.15 to 0.3 millimeters, and preferably 0.2millimeters, and is desirably formed from a conductive material, such asa stainless steel or the like. The captive washer 26 is used in thoseenvironments wherein it is desired to prevent the turning (torque)forces applied to tensioning the hollow screw 10 from rotating theassociated attachment or the like.

FIG. 13 is an alternative embodiment to those shown in FIGS. 11 and 12,and with respect to steps (220) and (224). FIG. 13 illustrates a hollowscrew work piece 80 formed as a result of the exclusion of the redrawstep (208), as mentioned above. In this respect the work piece 80includes only the constant diameter elongated body 12—the work piece 80otherwise does not include the relatively narrower redraw portion 48.Here, the free formed washer 72 is able to slide on to the elongatedbody 12 because the aperture 74 has a diameter slightly greater than theouter diameter of the elongated body 12. The work piece 80′ may then gothrough the same or substantially similar annealing step (218) androlling step (220), as described above. But, in this embodiment, sincethe elongated body 12 was of constant diameter, the resulting threadedportion 16 includes a series of threads 18 having an outer diametergreater than the outer diameter of the shank portion 14 and preferablywider than the diameter of the aperture 74 of the free formed washer 72.As such, the larger diameter threads 18 may capture the free formedwasher 72 with the integral washer 24 as shown, e.g., in FIG. 17, and inmore detail in the cross-sectional view of FIG. 24. Here, because theouter diameter of the threaded portion 16 was enlarged during therolling step (220) of the threads 18, the free formed washer 72 may freefloat along the shank portion 14, but remains captive between theintegral washer 24 and the threads 18. This feature may prevent the freeformed washer 72 from sliding off the elongated body 12 of the hollowscrew 10′ in the event the washer 72 is not mounted to the integralwasher 24 as part of step (224).

Alternatively, step (224) may be performed on the work piece 80′ wherebythe outer rim 78 of the free formed washer 72 is rolled up and over theintegral washer 24 substantially in accordance with step (224), andprior to steps (218)-(222). The work piece 80″ then goes through thesame or substantially similar annealing step (218) and rolling step(220), as described above. But, as described above, since the elongatedbody 12 was of constant diameter, the resulting threaded portion 16includes a series of threads 18 having an outer diameter greater thanthe outer diameter of the shank portion 14 and preferably wider than thediameter of the aperture 74 of the free formed washer 72. As such, thelarger diameter threads 18 may prevent the now captive washer 26 fromsliding off the elongated body 12 if the captive washer 26 happens todislodge from the integral washer 24.

In another aspect of the manufacturing process for making the varioushollow screws disclosed herein, FIG. 2 illustrates an additional andoptional step of deforming the threaded portion 16 to form a nose 82thereon (226). This step (226) is more specifically shown in FIG. 14,wherein a bottom 84 of the threaded portion 16 is inserted into aformation tool 86 having a generally tapering deformation aperture 88therein for generally reducing the diameter of the bottom 84 into theform shown with respect to the hollow screw 10″″″, and with respect tothe hollow screw 10″ in FIG. 18. In one embodiment, a spline keyedretention tool 90 may be inserted into the hollow shaft 22 to preventrotation thereof as the deformation aperture 88 generally forms the nose82, having the generally tapering characteristics shown in FIGS. 14 and18, at the bottom 84 of the threaded portion 16. Of course, this step(226) could be used to form the nose 82 on other embodiments, such asthe hollow screws 10, 10′, 10′″, 10″″, 10′″″ shown respectively in FIGS.16, 17 and 19-21.

In another aspect of the manufacturing process for making one or more ofthe hollow screws disclosed herein, FIG. 2 illustrates an additionaloptional step of stamping a bottom formed recess 92 into, e.g., the nose82. This stamping process (228) is generally shown with respect to FIG.15. Accordingly, the bottom formed recess 92 may be used in conjunctionwith or in place of either the outer polygonal shape 62 or the innerrecess 28 formed in the head 20. In this respect, various combinationsof the hollow screw may include one or more, or any combination of theouter polygonal shape 62, the inner recess 28 and/or the bottom formedrecess 92. Although, it is preferred that any such hollow screw includeat least one of the outer polygonal shape 62, the inner recess 28 or thebottom formed recess 92 to permit rotational tightening duringinstallation and release during removal.

FIGS. 16-21 illustrate various exemplary embodiments of the hollow screwas disclosed herein. For instance, FIG. 16 illustrates one embodiment ofthe hollow screw 10 including the elongated body 12 having the shankportion 14 of approximate equal length as the threaded portion 16, withthe flat bottom 84. This hollow screw 10 further includes the outerpolygonal shape 62 formed from the head 20 with the inner recess 28 inthe form of a spline recess (e.g., for use with a Torx or the like)formed therein. Accordingly, this hollow screw 10 may be screw tightenedwith one of a hex wrench, a spline wrench, or a combination tool forsimultaneous engagement with the polygonal shape 62 and the inner recess28. The head 20 also includes the integral washer 24 having the captivewasher 26 formed thereover.

FIG. 17 illustrates another embodiment of a hollow screw 10′, whereinthe elongated body 12 is relatively shorter than the hollow screw 10shown in FIG. 16. In this embodiment, the threaded portion 16 isrelatively longer in comparison to the smooth shank portion 14. The freeformed washer 72 is captured between the threaded portion 16 by thethreads 18 and the integral washer 24, as described above, and shown,e.g., more specifically in the cross-sectional view of FIG. 24. Similarto FIG. 16, this embodiment also includes the outer polygonal shape 62and the inner recess 28 in the form of a spline recess formed in thehead 20, and the bottom 84 is unformed or smooth. Accordingly, thishollow screw 10′ may be screw tightened with one of a hex wrench, aspline wrench, or a combination tool for simultaneous engagement withthe polygonal shape 62 and the inner recess 28.

FIG. 18 illustrates another alternative embodiment of a hollow screw10″, wherein the threaded portion 16 is relatively longer than the shankportion 14, similar to the embodiment shown above with respect to FIG.17. Although, in this embodiment, the head 20 is the generally smooth orflat head 54 and otherwise does not include the outer polygonal shape 62or the inner recess 28. Instead, the hollow screw 10″ includes thebottom formed recess 92 formed generally into the nose 82. In thisembodiment, the hollow screw 10″ may be screw tightened with a splinewrench via engagement with the bottom formed recess 92. Although, ofcourse, the bottom formed recess 92 could be formed at the bottom 84regardless whether the nose 82 is formed therein pursuant to step (226).Similarly, and alternatively, the nose 82 could be formed at the bottom84 without the bottom formed recess 92. This embodiment is particularlyconducive for flush mounting of the flat head 54 to the surroundingmounting surface (not shown). A cap (also not shown) may be insertedinto the hollow shaft 22 to close the interior from the surroundingenvironment, which may be particularly preferred in applications wherethe hollow screw 10″ is subject to airflow, such as the outside of anairplane (e.g., along the fuselage, wings, etc.).

FIG. 19 is another alternative embodiment of the hollow screw 10′″,wherein the threaded portion 16 and the shank portion 14 of theelongated body 12 are similar in size and structure as described abovewith respect to FIG. 16. In this embodiment, the head 20 is differentfrom the standpoint that it includes a rounded surface 94, as opposed tothe above-described outer polygonal shape 62. This rounded surface 94may be formed thereon as part of step (214), with a suitable stampingtool 64 of reciprocal size and shape, as opposed to stamping the outerpolygonal shape 62 thereon. In this embodiment, the hollow screw 10′″includes the inner recess 28 in the form configured to receive aPhillips head screwdriver.

FIG. 20 illustrates another alternative embodiment of the hollow screw10″″ similar to FIG. 16, excluding the captive washer 26. FIG. 21illustrates yet another variation of the hollow screw 10′″″, includingthe hollow shaft 22 formed by the elongated body 12 having the smoothshank portion 14 and the relatively longer threaded portion 16. In thisembodiment, the hollow screw 10′″″ includes a tapered head 20′ designedto seat flush with an outer mounting surface 96 as shown. Furthermore,the head 20′ is shown with the inner recess 28 configured for use with aPhillips screwdriver or the like for screw tight fitting therein.

Of course, each of the features described above, e.g., the length of theelongated body 12, the length and diameter of the shank portion 14 andthe threaded portion 16, including the threads 18, the size and shape ofthe head 20 (e.g., polygonal 62, flat 54, rounded 94, flush 20′, etc.),the inclusion (e.g., FIGS. 16, 17 and 20) or exclusion (e.g., FIGS. 18,19 and 21) of the integral washer 24, the inclusion (e.g., FIG. 16) orexclusion (e.g., FIGS. 17-21) of the captive washer 26, the inclusion(e.g., FIGS. 16, 17, 19 and 20) or exclusion (e.g., FIGS. 18 and 21) ofthe inner recess 28, the location and placement of the free formedwasher 72, formation of the nose 82 (e.g., FIG. 18) or use of the flatbottom 84 (e.g., FIGS. 16, 17 and 19-21), and/or the bottom formedrecess 92 (e.g., FIG. 18), may be mixed and matched with each other invarious different embodiments. While the present application disclosesvarious examples of these combinations, the scope and content of thepresent application should not be so limited to only those specificembodiments disclosed herein.

FIGS. 22-24 more specifically illustrate the above-mentioned embodimentsregarding the different diameter sizes of the shaft portion 14 relativeto the threaded portion 16 and the diametric size of the aperture 74 ofthe free formed washer 72. The embodiment illustrated in FIG. 22 wasformed as a result of the redraw step (208). In this respect, theelongated body 12 was further formed into two sections, namely the firstshank portion 14 having a first outside diameter relatively larger thanthe second relatively narrower redrawn portion 48 (FIG. 6). As a resultof the formation, the interior diameter “A” of the shank portion 14 isrelatively wider than the interior diameter “B” of the then formedredrawn portion 48. When the threads 18 are added as part of the rollingstep (220), the outer material of the redrawn portion 48 outwardlydeforms approximately ½ the difference between distance “A” and distance“B”. Put another way, the outside diameter of the shank portion 14 asmeasured by distance “C” is approximately the same distance as the outerdiameter of the peak-to-peak distance of the threads 18, as measured bydistance “D” after completion of the rolling step (220). Thus, the shankportion 14 and the threaded portion 16 have substantially the same outerdiameters.

FIGS. 22 and 23 are somewhat different in that the elongated body 12 wasnot subject to the redraw step (208) during the forming process. As aresult, the elongated body 12, and specifically the hollow shaft 22, hasa constant internal diameter, as identified by distance “E”. The resultis that the thread rolling step (220) again causes the material alongthe threaded portion 16 to deform outwardly to create the threads 18therein. This results in the threads 18 extending generally outwardly adistance greater than the outer diameter of the shank portion 14. Thisis best shown in FIGS. 24 and 25. Additionally, this extendeddiametrical distance may be used to capture and retain the free formedwasher 72 because the diametric distance of the aperture 74, as measuredby distance “F” in FIG. 24, is relatively smaller than the outerdiameter of the threads 18, as indicated by distance “G” also in FIG.24. Accordingly, in this embodiment, it is necessary to mount the freeformed washer 72 to the elongated body 12 before performing the rollingstep (220), as described above. Although, of course, another sized freeformed washer could be attached after the rolling step (220) as long asthe diameter of the aperture 74 is larger than the outside diameter “G”of the threads 18.

FIG. 25 illustrates another embodiment, wherein the hollow screw 10includes a wave washer 98. In this embodiment, the wave washer 98 couldbe crimped or sandwiched in between the integral washer 24 and thecaptive washer 26. The cross-sectional view of FIG. 26 illustrates thecross-section along line 26-26 in FIG. 25 with the captive washer 26added to sandwich the wave washer 98 therein with the integral washer24. The mounting process would be the same or similar to step (224),described above, except with the wave washer 98 sandwiched in between.

Similarly, the embodiments disclosed herein could be used to make ahollow nut 100, as shown in FIGS. 27 and 28, from a flat stock of metalmaterial or the like. FIG. 27 illustrates one embodiment wherein thehollow nut 100 includes a comparable body 12′ formed as part of one ormore formations, as described herein. Obviously, the body 12′ isrelatively shorter than the above-described elongated body 12 for use asa nut, but the same basic formation procedures apply. Furthermore, thebody 12′ may include a set of female or internal threads 102 bythreading the body 12′ using processes known in the art. Similar to theabove, the hollow nut 100 also includes the generally outwardlyextending radial flange 104 (comparable to the integral washer 24) madeas per, e.g., comparable steps (210) and (212), for select mounting of acaptive washer 26′ in accordance with the embodiments described above(e.g., a comparable step (224)). FIG. 28 is a similar embodiment, butincluding a wave washer 98′ crimped or sandwiched between the outwardlyextending radial flange 104 and the captive washer 26′, in accordancewith a similar or comparable step (224). The nut 100 may also go througha comparable annealing step (218) to soften the nut 100 to form theinternal threads 102 and a comparable hardening step (222) to ensurerigidity and longevity.

A variety of further modifications and improvements in and to the hollowscrew and the method of making the same will be apparent to personsskilled in the art. By way of example, either one of the inner and outerpolygonal shapes can be omitted, or both can be performed in a singlestamping step. Alternately, in lieu of the internal drive recessdescribed above, such as a Phillips or Torx recess, other forms ofstandard drive recesses or polygonal recesses could be formed therein.The annealing and hardening steps can also be varied. Accordingly, nolimitation on the invention is intended by way of the foregoingdescription and accompanying drawings.

What is claimed is:
 1. A hollow screw, comprising: a head formed from acorrosion resistant flat stock metal material comprising A286 steel; anelongated and hollow shaft having a wall thickness between about 0.2 toabout 0.7 millimeters formed from the corrosion resistant flat stockmetal material and extending from the head, the elongated and hollowshaft including a shank portion and a threaded portion having aplurality of threads thereon, the threads having a strength betweenabout 1200 MPa to 1400 MPa; and a rotational engagement mechanismcomprising a polygonal shape or a recess formed from the head or theelongated and hollow shaft, and configured to permit tightening of thehollow screw by way of the threads.
 2. The hollow screw of claim 1,including an integral washer formed from the head and having an enlargedhorizontal and generally circular surface area radially extendingoutwardly from the head.
 3. The hollow screw of claim 2, a captivewasher positioned adjacent the enlarged horizontal and generallycircular surface area and having an outer rim bent generally about anouter periphery of the integral washer at least partially sandwichingthe integral washer therein, the captive washer configured to rotatefreely about the integral washer.
 4. The hollow screw of claim 3,wherein the captive washer comprises a thickness of 0.15 to 0.30millimeters and comprises a conductive material.
 5. The hollow screw ofclaim 1, wherein the rotational engagement mechanism is formed from thecorrosion resistant flat stock metal material and the polygonal shapecomprises a hexagonal head or the recess comprises a spline recess. 6.The hollow screw of claim 1, wherein the elongated and hollow shaftincludes a capped and tapered nose having a spline recess therein at anend opposite the head, wherein the head comprises a round head, a flathead, or a tapered head.
 7. A method for making a hollow screw,comprising the steps of: forming a shallow cup having a radiallyoutwardly extending rough cut flange at one end thereof from a generallyflat metal material; extruding an elongated and hollow body from theshallow cup; clipping and flattening the generally radially outwardlyextending rough cut flange to the desired size and shape of a screwhead; annealing to soften at least the elongated and hollow body;rolling a plurality of threads to at least a portion of the exterior ofthe softened elongated and hollow body, thereby forming the elongatedand hollow body into a substantially smooth shank portion and a threadedportion; and hardening the hollow screw.
 8. The method of claim 7,including the step of stamping a relatively circular blank from a rollstock of the flat metal material comprising a corrosion resistant A286steel.
 9. The method of claim 1, wherein the elongated and hollow bodycomprises a wall thickness of about 0.2 to about 0.7 millimeters. 10.The method of claim 7, including the step of redrawing the elongated andhollow body into a shank portion and a redraw portion having an outerdiameter relatively narrower than an outer diameter of the shankportion.
 11. The method of claim 7, including the steps of: invertingthe screw head into a generally central curved dome with an outwardlyextending skirt; reconing the central curved dome into an outerpolygonal shape; and stamping the skirt into an integral washer.
 12. Themethod of claim 11, including the step of forming a captive washer overthe integral washer in rotatable relation therewith.
 13. The method ofclaim 7, including the step of imparting an inner spline or Philipsrecess to the screw head.
 14. The method of claim 7, wherein theannealing step includes the step of heating the hollow screw for about 1hour at an elevated temperature of about 950-980 degrees Celsius,wherein the hollow screw comprises a hardness of about 79 Rockwell Bafter the annealing step.
 15. The method of claim 7, including the stepof inserting a stability pin into the elongated and hollow body duringthe rolling step, the stability pin comprising an outer diameterapproximately the size of an inside diameter of the threaded portion ofthe elongated and hollow body, the stability pin supporting theperipheral wall thereof to prevent collapsing during the rolling step.16. The method of claim 7, wherein the hardening step includes the stepof heat treating the hollow screw by precipitation hardening for about16 hours at a temperature of about 690-720 degrees Celsius.
 17. Themethod of claim 7, wherein the hollow screw comprises a hardness ofabout 42 Rockwell C and the threads comprise a strength of about1200-1400 MPa after the hardening step.
 18. The method of claim 7,including the step of forming a rounded nose from one end of theelongated and hollow body.
 19. The method of claim 7, including the stepof keying a bottom formed recess into a closed end of the elongated andhollow body.
 20. The method of claim 7, wherein the hollow screwcomprises a weight of about ½ the weight of a solid core screw ofsufficient thread strength.
 21. A method for making a hollow screw,comprising the steps of: forming an elongated and hollow body having awall thickness of about 0.2 to about 0.7 millimeters from a generallyflat metal material; clipping and flattening one end of the elongatedand hollow body into a desired size and shape of a screw head; annealingfor about 1 hour at an elevated temperature of about 950-980 degreesCelsius to soften the elongated and hollow body and the screw head;rolling a plurality of threads to at least a portion of the exterior ofthe softened elongated and hollow body; and hardening the hollow screwto a hardness comprising 42 Rockwell C, wherein the threads comprise astrength of about 1200-1400 MPa.
 22. The method of claim 21, includingthe step of stamping a relatively circular blank from a roll stock ofthe flat metal material comprising corrosion resistant material A286steel.
 23. The method of claim 21, including the step of redrawing theelongated and hollow body into a shank portion and a redraw portionhaving an outer diameter relatively narrower than an outer diameter ofthe shank portion.
 24. The method of claim 21, including the steps of:inverting the screw head into a generally central curved dome with anoutwardly extending skirt; reconing the central curved dome into anouter polygonal shape; and stamping the skirt into an integral washer.25. The method of claim 24, including the steps of inserting a freeformed washer over the elongated and hollow body and bending an outerrim thereof over an outer periphery of the integral washer to at leastpartially sandwich the integral washer therein.
 26. The method of claim25, including the step of stamping a spline recess to the screw head.27. The method of claim 21, including the step of inserting a stabilitypin into the elongated and hollow body during the rolling step, thestability pin including an outer diameter approximately the size of aninside diameter of the threaded portion of the elongated and hollowbody, the stability pin supporting the peripheral wall to preventcollapsing during the rolling step.
 28. The method of claim 21,including the step of forming a rounded nose from one end of theelongated and hollow body and keying a bottom formed recess into thenose.
 29. A method for making a hollow screw, comprising the steps of:forming a shallow cup and a radially outwardly extending rough cutflange from a generally circular flat metal material; extruding anelongated and hollow body from the shallow cup; clipping and flatteningthe generally radially outwardly extending rough cut flange to thedesired size and shape of a screw head; inverting the screw head into acentral curved dome with an outwardly extending skirt; reconing thecentral curved dome into a polygonal shape; stamping the skirt into anintegral washer; annealing to soften at least the elongated and hollowbody; inserting a stability pin into the elongated and hollow body, thestability pin comprising an outer diameter approximately the size of aninside diameter of the elongated and hollow body, the stability pinsupporting the peripheral wall therein; rolling a plurality of threadsto at least a portion of the exterior of the softened elongated andhollow body; stamping a spline recess to the screw head; and hardeningthe hollow screw.
 30. The method of claim 29, including the step ofredrawing the elongated and hollow body into a shank portion and aredraw portion having an outer diameter relatively narrower than anouter diameter of the shank portion.
 31. The method of claim 29,including the steps of: stamping a relatively circular blank from a flatroll stock of corrosion resistant material comprising A286 steel,wherein the elongated and hollow body comprises a wall thickness ofabout 0.2 to about 0.7 millimeters; heating the hollow screw for about 1hour at an elevated temperature of about 950-980 degrees Celsius; andprecipitation hardening the hollow screw for about 16 hours at atemperature of about 690-720 degrees Celsius, wherein the hollow screwcomprises a hardness of about 42 Rockwell C and the threads comprise astrength of about 1200-1400 MPa after the precipitation hardening step.32. The method of claim 29, including the steps of inserting a washerover the elongated and hollow body before the rolling step, the washerconfigured to free float between the integral washer and the threads.33. The method of claim 32, including the steps of forming a roundednose from one end of the elongated and hollow body and keying a bottomformed recess into the nose.